This invention relates to a movable blade pump comprising an actuating mechanism disposed in a suction casing below an impeller for varying angular positions of blades.
In movable blade diagonal flow pumps of the prior art, hydraulic fluid is filled in impeller boss which is closed to the outside and contains therein a crosshead and a connecting shaft for converting a reciprocatory movement of an actuating shaft to a rotational movement of the blades. The actuating shaft extends through a main hollow shaft and is connected to a piston in an upper hydraulic cylinder. A motor shaft disposed above the hydraulic cylinder is also hollow, and working fluid passages extend through the motor shaft to be connected to the upper and the lower ends of the hydraulic cylinder. There are provided means for supplying working fluid to these passages from a control located above the motor, and means for effecting feedback control of the position of the hydraulic piston. With this arrangement, the mechanism for transmitting the reciprocatory movement of the actuating shaft to the blades is built in an impeller boss which is filled with hydraulic fluid, so that the hydraulic fluid protects the inside of the impeller boss from invasion of water and other foreign matter outside which may occur corrosion and abrasion, and it provides a good lubricating characteristics. However, some disadvantages are encountered with this arrangement. More specifically, the need to use an elongated actuating shaft and a hollow main shaft and a hollow motor shaft makes fabrication and assembly difficult, thereby increasing cost. Also, the provision of a control on the top of the motor increases the height of the pump above the ground level, so that the pump tends to vibrate. Therefore, there have been a possibility that the hydraulic fluid in the impeller boss leaks and finds its way into the fluid handled by the pump or the fluid handled by the pump enters in the hydraulic fluid.